January 4, 2004

The Pakistani leaders who denied for years that scientists at the country's secret A. Q. Khan Research Laboratories were peddling advanced nuclear technology must have been averting their eyes from a most conspicuous piece of evidence: the laboratory's own sales brochure, quietly circulated to aspiring nuclear weapons states and a network of nuclear middlemen around the world.

The cover bears an official-looking seal that says "Government of Pakistan" and a photograph of the father of the Pakistani bomb, Abdul Qadeer Khan. It promotes components that were spinoffs from Pakistan's three-decade-long project to build a nuclear stockpile of enriched uranium, set in a drawing that bears a striking resemblance to a mushroom cloud.

In other nations, such sales would be strictly controlled. But Pakistan has always played by its own rules.

As investigators unravel the mysteries of the North Korean, Iranian and now the Libyan nuclear projects, Pakistan ó and those it empowered with knowledge and technology they are now selling on their own ó has emerged as the intellectual and trading hub of a loose network of hidden nuclear proliferators.

That network is global, stretching from Germany to Dubai and from China to South Asia, and involves many middlemen and suppliers. But what is striking about a string of recent disclosures, experts say, is how many roads appear ultimately to lead back to the Khan Research Laboratories in Kahuta, where Pakistan's own bomb was developed.

In 2002 the United States was surprised to discover how North Korea had turned to the Khan laboratory for an alternative way to manufacture nuclear fuel, after the reactors and reprocessing facilities it had relied on for years were "frozen" under a now shattered agreement with the Clinton administration. Last year, international inspectors and Western intelligence agencies were surprised again, this time by the central role Pakistan played in the initial technology that enabled Iran to pursue a secret uranium enrichment program for 18 years.

The sources of Libya's enrichment program are still under investigation, but those who have had an early glance say they see "interconnections" with both Pakistan and Iran's programs ó and Libyan financial support for the Pakistani program that stretches back three decades.

Until two weeks ago, Pakistani officials had long denied that any nuclear technology was transferred from their laboratories. But now that story has begun to change, after the Pakistani authorities, under pressure, began interrogating scientists from the laboratory about their assistance to other nuclear aspirants. Two weeks ago, Dr. Khan himself was called in for what appears to have been a respectful, and still inconclusive, questioning.

Responding to requests relayed through associates, Dr. Khan has recently denied that he aided atomic hopefuls. But American and European officials note that in the 1980's he repeatedly denied that Pakistan was at work on an atomic bomb, which it finally tested in 1998.

While American intelligence officials have gathered details on the activities of the creator of the Pakistani bomb and his compatriots for decades, four successive American presidents have dealt with the issue extremely delicately, turning modest sanctions against Pakistan on and off, for fear of destabilizing the country when it was needed to counter the Soviets in the 1980's, much as it is needed to battle terrorism today.

President Bush, who regularly talks about nuclear dangers, has never mentioned Pakistan's laboratories or their proliferation in public ó probably out of concern of destabilizing President Pervez Musharraf, who has survived two assassination attempts in December.

"He's been a stand-up guy when it comes to dealing with the terrorists," Mr. Bush said of General Musharraf on Thursday. "We are making progress against Al Qaeda because of his cooperation." He dismissed a question about the vulnerability of Pakistan's own nuclear weapons, saying, "Yes, they are secure," then changed the subject.

Yet when President Bush talks about the horrors that could unfold if a nuclear weapon fell into the hands of terrorists, it is Pakistan's combustible mix of expertise, components, fuel and fully assembled weapons that springs to the minds of American and European intelligence experts. In public, the White House says it has received "assurances" from Pakistan that if there ever were nuclear exports they are finished.

"There is this almost empty-headed recitation of assurances that whatever Pakistan did in the past it's over, it's no longer a problem," said one senior European diplomat with access to much of the intelligence about proliferation. "But there's is no evidence that it has ever stopped."

Mohamed ElBaradei, the director general of the International Atomic Energy Agency, the United Nations organization charged with monitoring nuclear energy worldwide, contends that the recent nuclear disclosures show that the system put in place at the height of the cold war to contain nuclear weapons technology has ruptured and can no longer control the new nuclear trade.

"The information is now all over the place, and that's what makes it more dangerous than in the 1960's," Dr. ElBaradei said.

The Crucial Ingredient

The biggest hurdle in making a nuclear weapon is not designing the warhead, but getting the right fuel to create an atomic explosion. One route is to extract plutonium from nuclear reactors and reprocess it to produce more fuel, known as creating a fuel cycle. The other is to extract uranium from the ground and enrich it.

The 1970 treaty on the nonproliferation of nuclear weapons was devised to control which countries could possess and pursue nuclear arms. It allowed the United States, Britain, France, the Soviet Union and China to keep all their weapons but required all other signatories to forswear nuclear arms. North Korea, Iran and Libya all signed, allowing I.A.E.A. inspectors limited visits to verify that countries producing nuclear fuel were truly using "atoms for peace." Pakistan and India never signed, nor did Israel.

Aside from inspections, spy satellites and airborne "sniffers" can usually pick out the huge complexes needed to extract spent fuel from nuclear reactors and turn it into bomb fuel. But after North Korea was caught cheating by the United States in the early 1990's and was forced into an agreement to "freeze" its reactor-and-reprocessing complex at Yongbyon, the lesson was clear: to produce bomb fuel, countries needed to take a more surreptitious route.

Uranium enrichment was the most promising, because it could take place in hidden facilities, emitting few traces. And that was the technology that Dr. Khan perfected as his laboratory raced to produce a nuclear bomb to keep up with its rival, India.

The key to the technology is the development of centrifuges. These hollow tubes spin fast to separate a gaseous form of natural uranium into U-238, a heavy isotope, and U-235, a light one. The rare U-235 isotope is the holy grail: it can easily split in two, releasing bursts of nuclear energy.

But making centrifuges is no easy trick. The rotors of centrifuges, spinning at the speed of sound or faster, must be very strong and perfectly balanced or they fly apart catastrophically.

To produce bomb-grade fuel, uranium must pass through hundreds or thousands of centrifuges linked in a cascade, until impurities are spun away and what remains is mainly U-235 . The result is known as highly enriched uranium.

Dr. Khan returned to Pakistan in 1976 after working in the Netherlands, carrying extremely secret centrifuge designs ó a Dutch one that featured an aluminum rotor, and a German one made of maraging steel, a superhard alloy. He was charged with stealing the designs from a European consortium where he worked.

"The designs for the machines," said a secret State Department memo at the time, "were stolen by a Pakistani national."

The steel rotor in the German design turned out to be particularly difficult to make, but it could spin twice as fast, meaning it produced more fuel.

Dr. Khan's accomplishments turned him into a national hero. In 1981, as a tribute, the president of Pakistan, Gen. Mohammad Zia ul-Haq, renamed the enrichment plant the A. Q. Khan Research Laboratories.

Dr. Khan, a fervent nationalist, has condemned the system that limits legal nuclear knowledge to the five major nuclear powers, or that has ignored Israel's nuclear weapon while focusing on the fear of an Islamic bomb. "All Western countries," he was once quoted as saying, "are not only the enemies of Pakistan but in fact of Islam."

In the years before Pakistan's first test in 1998, Dr. Khan and his team began publishing papers in the global scientific literature on how to make and test its uranium centrifuges. In the West, these publications would have been classified secret or top secret.

But Dr. Khan made no secret of his motive: he boasted in print of circumventing the restrictions of the Western nuclear powers, declaring in a 1987 paper that he sought to pierce "the clouds of the so-called secrecy." Papers in 1987 and 1988 detailed how to take the next, difficult steps in the construction of centrifuges ó reaching beyond first-generation aluminum rotors to produce more efficient centrifuges out of maraging steel.

David Albright, a former weapons inspector for the I.A.E.A, said the American intelligence community viewed Dr. Khan's papers as a boast. They proved that Pakistan "knew how to build the G-2," a particularly complex design of German origin.

A 1991 paper by his colleagues at the laboratory gave more details away, revealing how to etch special grooves on a centrifuge's bottom bearing, a crucial part for aiding the flow of lubricants in machines spinning at blindingly fast speeds.

A Pentagon program that tracks foreign scientific publications has uncovered dozens of reports, scientific papers and conference proceedings on uranium enrichment that Dr. Khan and his colleagues published. While federal and private experts agree that the blitz left much confidential ó including some crucial dimensions, ingredients, manufacturing tricks and design secrets ó Pakistan was clearly proclaiming that it had mastered the black art.

"It was a signal to India and the West saying, `Look, we're not the backward people you think we are,' " said Mark Gorwitz, a nonproliferation expert who tracks the Pakistani literature.

The scientific papers were soon followed by sales brochures. Much of the gear marketed by the Khan laboratory was critical for anyone eager to make Dr. Khan's kind of centrifuges. It included vacuum devices that attached to a centrifuge casing and sucked out virtually all the air, reducing friction around the spinning rotors.

In 2000, the Pakistani government ran its own advertisement announcing procedures for commercial exports of many types of nuclear gear, including gas centrifuges and their parts, according to a Congressional Research Service report published in May. Many of the items, it noted, "would be useful in a nuclear weapons program."

Former American intelligence and nonproliferation experts said the C.I.A. was aware of some, but not all, of these activities, and began tracking scientists at the Khan laboratory.

But at every turn, overt pressure was weighed against strategic interests. In the 1980's, Washington viewed Pakistan as a critical ally in the covert war it was waging against the Soviets in Afghanistan. By 1986, American intelligence agencies concluded that Pakistan had succeeded in making weapon-grade uranium, the sure sign that the centrifuges worked. But that same year, Mr. Reagan announced an aid package to Pakistan of more than $4 billion.

The First Nuclear Deals

What American intelligence agencies apparently did not understand at the time was the pace at which Dr. Khan's team was beginning to help other nations.

It started as a quid pro quo with an old patron: China. A declassified State Department memo, obtained by the National Security Archive in Washington, concluded that China, sometime after its first bomb tests in the mid-1960's, had provided Pakistan technology for "fissile material production and possibly also nuclear device design."

Years later, the flow reversed. Mr. Albright, who is the president of the Institute for Science and International Security, an arms control group in Washington, has concluded that China was an early recipient of Pakistan's designs for centrifuges. China had used an antiquated, expensive process for enriching uranium, and the technology Dr. Khan held promised a faster, cheaper, more efficient path to bomb-making.

But that was just the start. Evidence uncovered in recent months shows that around 1987 Pakistan struck a deal with Iran, which had tried unsuccessfully to master enrichment technology on its own during its war with Iraq. The outlines of the deal ó pieced together from limited inspections and documents turned over to the I.A.E.A. in October ó show that a centrifuge of Pakistani design finally solved Iran's technological problems. That deal was "a tremendous boost," Mr. Albright and his colleague, Corey Hinderstein, said in a draft report on the Iranian program. "The possession of detailed designs could allow Iran to skip many difficult research steps," they added.

The Iranian documents turned over to the I.A.E.A. make no reference to Pakistan itself; they only point to its signature technologies.

"We have middlemen and suspicions," said a Western diplomat with access to the documents. "There is a Pakistani tie for sure, but we don't know the details."

Iran's program fooled the I.A.E.A., which caught no whiff of it during 18 years of inspections. But Pakistan's role was also well hidden from American intelligence agencies.

"We had some intelligence successes with Iran, we knew about some of their enrichment efforts," said Gary Samore, who headed up nonproliferation efforts in the Clinton administration's National Security Council. "What we didn't know was the Pakistan connection ó that was a surprise. And the extent of Pakistan's ties was, in retrospect, the surprise of the 1990's."

The Iranians were hardly satisfied customers. They had gotten Pakistan's older models and were forced to slog ahead slowly for two decades, foraging around the world for parts, building experimental facilities involving a few hundred centrifuges, but apparently failing to produce enough fissile material for a bomb.

If the Iranians were the turtle, the North Koreans proved the hare. Around 1997, a decade after the Pakistani deal with Iran, Dr. Khan made inroads with the government of Kim Jong Il, as it sought a way to make nuclear fuel away from the Yongbyon plant and the prying eyes of American satellites. Dr. Khan began traveling to North Korea, visiting 13 times, American intelligence officials said.

During those visits, North Korea offered to exchange centrifuge technology for North Korean missile technology, enabling Pakistan to extend the reach of its nuclear weapons across India.

Again, American intelligence agencies missed many of the signals. They knew of an experimental program, but it took evidence from South Korea to demonstrate that North Korea was moving toward industrial-level production. Then in the summer of 2001, American spy satellites spotted missile parts being loaded into a Pakistani cargo plane near Pyongyang, the North Korean capital. The parts were assumed to be the quid pro quo for the nuclear technology.

Last spring, a few months after the deal was revealed in The New York Times, the State Department announced some sanctions against the Khan laboratory but cited the illegal missile transactions. The State Department said it had insufficient evidence to issue sanctions for a nuclear transfer, a move some dissenting officials suspected was a concession to avoid embarrassing General Musharraf, who had denied that any nuclear transfers ever occurred.

A Congressional report on the Pakistan-North Korea trade notes that over the years "Pakistan has been sanctioned in what some observers deem, an `on again, off again' fashion," mostly for importing technology for unconventional weapons, and later for its 1998 nuclear tests. Those sanctions, which were also issued against India, were waived shortly after the Sept. 11, 2001, terrorist attacks, when the United States suddenly needed Pakistan's cooperation.

It is unclear whether the Pakistan-North Korea connection has been cut off. But new evidence suggests that North Korea is still racing ahead. In April, a ship carrying a large cargo of superstrong aluminum tubing was stopped in the Suez Canal after the German authorities determined that it was destined for North Korea. The precise size of the tubes, according to Western diplomats and industry reports, suggested that they were intended for making the outer casings of G-2 centrifuges, the kind whose rotors are made of steel, and that Dr. Khan wrote about.

The C.I.A. estimates that by 2005, if unchecked, North Korea will begin large-scale production of enriched uranium.

But so far, American intelligence agencies say they are uncertain where North Korea's centrifuge operations are. On Friday, North Korea said it would allow a delegation of American experts into the country this week.

Halting Nuclear Trades

Early in 2003, Mr. Bush established a coordinating group inside the White House to oversee the interception of shipments of unconventional weapons around the world. So far, Washington has drawn more than a dozen nations into a loose posse to track and stop shipments, and Germany, Italy, Taiwan and Japan have executed seizures.

But the first interceptions ó and the trail of parts and agreements they reveal ó have only pointed to the mushrooming size of the secondary market in parts.

Even more worrisome are the kinds of exchanges that do not move on ships and planes, what Ashton B. Carter, who worked in the Clinton administration on North Korean issues, calls "substantial technical cooperation among all members of the brotherhood of rogues."

North Korean engineers have been sighted living in Iran, ostensibly to help the country build medium- and long-range missiles. But the growing suspicion is that the relationship has now expanded beyond missiles, and that the two nations are warily dealing in the nuclear arena as well.

"We're debating the evidence," said one administration official.

The latest nuclear disclosures came after the United States spotted a German-registered ship headed for Libya through the Suez Canal, with thousands of parts for uranium centrifuges. The interception in October of that shipment, American officials say, tipped the balance for the Libyan leader, Col. Muammar el-Qaddafi, forcing him to agree in December to disclose and dismantle his own nuclear program.

Inspectors are still investigating where Libya's components came from, focusing on manufacturers in Europe and what Dr. ElBaradei calls "interconnections" between the Libyan program and Iran's.

The intercepted shipment came from Dubai, a place of great importance in Dr. Khan's secretive world. It was a Dubai middleman claiming to represent Dr. Khan who in 1990, on the eve of the Persian Gulf war, offered Dr. Khan's aid to Iraq in building an atom bomb. And it was a Dubai middleman whom Dr. Khan blamed for supplying centrifuge parts to Iran, said a European confidante of Dr. Khan's who spoke on the condition of anonymity.

Ties between Libya and Pakistan go back years. In 1973, when Pakistan was just starting its nuclear program, Libya signed a deal to help finance its atomic efforts in exchange for knowledge about how to make nuclear fuel, said Leonard S. Spector of the Monterey Institute of International Studies' Center for Nonproliferation Studies. From 1978 to 1980, he added, Libya appears to have supplied Pakistan with uranium ore. But Libya appears to have made much less progress than the Iranians had.

Dr. ElBaradei estimates that 35 to 40 nations now have the knowledge to build an atomic weapon. In place of the nonproliferation treaty, which he calls obsolete, he proposes revising the world's system to place any facilities that can manufacture fissile material under multinational control.

"Unless you are able to control the actual acquisition of weapon-usable material, you are not able to control proliferation," he said in recent interview. But Mr. Bush and the leaders of the other established nuclear states are reluctant to renegotiate a stronger treaty because it will reopen the question of why some states are permitted to hold nuclear weapons and others are not.

For now the world is left watching a terrifying race ó one that pits scientists, middlemen and extremists against Western powers trying to intercept, shipload by shipload, the technology as it spreads through the clandestine network. Mr. Bush remains wary of cracking down on a fragile Pakistan, for fear pressure could tip the situation toward the radicals.

Some in the administration say they think other nations may follow Libya's calculations and abandon their programs voluntarily. But there are doubters.

"Its a fine theory," a top nonproliferation strategist in the administration said recently. "The question for 2004 is whether the mullahs or Kim Jong Il buy into it."

David Rohde contributed reporting from Pakistan for this article.